Managing organic waste streams is a major challenge for the agricultural industry. Anaerobic digestion (AD) of organicwastes is a preferred option in the waste management hierarchy, as this processcangenerate renewableenergy, reduce emissions from wastestorage, andproduce fertiliser material.However, Nitrate Vulnerable Zone legislation and seasonal restrictions can limit the use of digestate on agricultural land. In this paper we demonstrate the potential of cultivating microalgae on digestate as a feedstock, either directlyafter dilution, or indirectlyfromeffluent remaining after biofertiliser extraction. Resultant microalgal biomass can then be used to produce livestock feed, biofuel or for higher value bio-products. The approach could mitigate for possible regional excesses, and substitute conventional high-impactproducts with bio-resources, enhancing sustainability withinacircular economy. Recycling nutrients from digestate with algal technology is at an early stage. We present and discuss challenges and opportunities associated with developing this new technology.

This research presents a conceptual model to illustrate how people living in rural areas can harness bioenergy to create beneficial ‘community-driven’ income-generating activities. The research is contextualised within the rural developing areas of Bangladesh where people live in abject poverty and energy deficiency. The research methodology applied in this study aims to determine the basic requirements for implementing community-based anaerobic digestion (AD) facilities and illustrate how an AD facility positively impacts upon the lives of rural communities directly after its installation. The survey results demonstrate that implementing a biogas plant can save 1 h and 43 min of worktime per day for a rural family where women are generally expected to for cook (by the long-term tradition). In addition to the positive impacts on health and climate change through adoption of clean energy generation, this time saving could be utilised to improve women′s and children’s education. The research concludes that, by providing easy access to clean bioenergy, AD can change people’s quality of life, yielding major social, economic and environmental transformations; key benefits include: extending the working day; empowering women; reducing indoor air pollution; and improving people’s health and welfare. Each of these tangible benefits can positively contribute towards achievement of the UN’s Sustainable Development Goals. This work demonstrates the potential to increase the implementation of AD systems in other developing world countries that have similar geographic and socioeconomic conditions.

In this study, the biomethane potential of five agricultural crop residues (ACR's) (rice straw, vegetable waste, maize straw, coffee husk and oil palm empty fruit bunches (OPEFB)) and five Fruit-Based Agro-Industrial Wastes (FBAIW's) (jackfruit straw, banana, orange, apple and pineapple peel waste) were evaluated. The carbon and energy balance for each waste was also theoretically modelled for two biogas conversion scenarios (AD with CHP or biogas upgrading). A standard biomethane potential test (BMP) was operated over 30 days at 37 o C. Specific methane potential (SMP) of FBAIW's was generally higher than that of the ACR's, except for vegetable waste. Vegetable waste was identified as having the highest SMP (0.420 m 3 /kgVS added ). With respect to ACRs, OPEFB and coffee husk had the lowest SMP values of 0.185 and 0.181 m 3 /kgVS added , respectively. This was attributed to the higher lignin content of these wastes which can impact on biodegradation and subsequent biogas production. Theoretical estimations showed a positive energy balance for all wastes tested. In terms of exportable energy, apple peel waste was shown to have the highest exportable energy potential. The FBAIW's also exhibited greater emissions savings than ACR's (with the exception of vegetable waste). This study concluded that there is good potential to valorise these wastes using AD and that this could address the challenges of waste management and clean energy provision in Indonesia.

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Calculations towards determining the greenhouse gas mitigation capacity of a small-scale biogas plant (3.2 m plant) using cow dung in Bangladesh are presented. A general life cycle assessment was used, evaluating key parameters (biogas, methane, construction materials and feedstock demands) to determine the net environmental impact. The global warming potential saving through the use of biogas as a cooking fuel is reduced from 0.40 kg CO equivalent to 0.064 kg CO equivalent per kilogram of dung. Biomethane used for cooking can contribute towards mitigation of global warming. Prior to utilisation of the global warming potential of methane (from 3.2 m biogas plant), the global warming potential is 13 t of carbon dioxide equivalent. This reduced to 2 t as a result of complete combustion of methane. The global warming potential saving of a bioenergy plant across a 20-year life cycle is 217 t of carbon dioxide equivalent, which is 11 t per year. The global warming potential of the resultant digestate is zero and from construction materials is less than 1% of total global warming potential. When the biogas is used as a fuel for cooking, the global warming potential will reduce by 83% compare with the traditional wood biomass cooking system. The total 80 MJ of energy that can be produced from a 3.2 m anaerobic digestion plant would replace 1.9 t of fuel wood or 632 kg of kerosene currently used annually in Bangladesh. The digestate can also be used as a nutrient rich fertiliser substituting more costly inorganic fertilisers, with no global warming potential impact.